Who has time to spend doing some fancy eye contouring? I love a simple fail-proof product that you can keep in your bag and use with your fingers. This color is gorgeous and you can build it up or wear it light.

I'm a sucker for voluminous hair! This product really creates volume at the roots. I use it to lift me up at the end of a long day, or to create a more stable and volume-packed party ponytail. It fits in all purses and makes such a difference.

What did we do before these hair ties?! Pre-Twistband, I'd always have marks on my wrists and dents in my hair. These are cute and they do the job sans dent. I also love the little charms they added to these -- it looks great on your wrist!

Guest editor Katia Beauchamp knows a lot more about beauty than your average Harvard Business School grad and entrepreneur. After all, she's the founder of Birchbox -- you know, that company that sends the cute little box full of amazing product samples every month. It's kind of like a department store beauty counter delivered straight to your mailbox.

After three years at the helm of Birchbox, it's safe to say Katia knows her stuff when it comes to beauty. Taking full advantage of her guest editorship, we asked Katia to share her favorite products -- the ones she's discovered along the way and just can't live without. From her favorite mascara to the ultimate nude nail polish, we've got the scoop right here.